In agriculture, farm sprayers, chemical applicators, seeders and other machinery are drawn or propelled over the ground. The ground is generally uneven, and often quite rough. In the operation of the machinery or equipment, it is essential that the area covered by the operation of the equipment, e.g. a fertilizer sprayer, is as contiguous as practically possible to an area already treated. It is obvious that overlapping would result in a loss of the medium (e.g. fertilizer or seed) distributed by the machinery, or an excessive application of the medium (deleterious to the cultivation), or both. On the other hand, leaving an untreated area would result in losses due to incomplete treatment. In other words, due to costs of the materials and the need to properly control the vegetation, insects etc., high application or treatment efficiency must be sought.
Typically, an operator of the vehicle watches the proximity of a specific working implement of the vehicle, e.g. the end of a sprayer boom, to the edge of a previously sprayed strip. The operator adjusts the direction of the vehicle accordingly. To facilitate the operator's task of viewing the boundary of the previously treated area, or another predetermined boundary, e.g. the edge of the field, it has already been proposed to apply an optical marking at the edge of the boundary. An example of an apparatus for such purpose is described in U.S. Pat. No. 3,339,843 issued Sep. 5, 1967 to Horton. A dye is sprayed at the end of a sprayer boom which is carried by a vehicle. The operator adjusts the direction of the vehicle while viewing the marking left by the dye.
This task becomes arduous or virtually impossible as the size of the working implement, e.g. the length of a working boom, becomes significant. Agricultural machinery now in use can reach the span in the range of 240 feet (or 120 feet boom length on each side of the vehicle). The accuracy of visually determining the position of the marking by the operator diminishes with distance between the operator and the marking. The view of the marker may also become obscured by the vegetation.
U.S. Pat. No. 3,211,381 to Rasmussen teaches discharging a chemical marker with the material being spread or sprayed.
U.S. Pat. No. 4,011,914 to Elmer shows a device for physically marking the outer limits of the sprayer boom, having a sled-type marking means at the extremities of the spreader.
Other marking arrangements are disclosed in U.S. Pat. No. 4,526,236 to Jacobsen, U.S. Pat. Nos. 5,429,061 and 5,666,893 to Bourgeois, U.S. Pat. No. 5,338,129 to Oden and U.S. Pat. No. 5,133,500 to Simpson. The Oden and Simpson patents teach the use of a colored foam to mark various surfaces.
A crop sensing device is disclosed in U.S. Pat. No. 5,279,068 to Rees. The device uses infra-red (IR) transmitters and receivers to position the agricultural equipment in the correct position relative to rows of plants. IR beams are used to activate actuators to move the tools to the desired relationship with the rows.
Control of individual spray nozzles using separate near-infrared transmitters and receivers is proposed in U.S. Pat. No. 5,222,324 to O'Neall.
A non-contact radiant energy device is presented in U.S. Pat. No. 5,176,320 to Krauss for controlling the amount of water applied during snowmaking.
U.S. Pat. No. 5,155,683 to Rahim proposes a remote control guidance system to maneuver equipment around obstacles using a television camera to send images of the area to a screen at the vehicle operator's station.
A system for determining the position of a vehicle on highways described in U.S. Pat. No. 5,351,044 to Mathur. This system is quite complicated and not suitable for the agricultural field environment.
To summarize, the prior art teaches various ways to mark the boundary of an agricultural processed area to avoid an overlap or incomplete coverage in further operation. The art assumes that the boundary can be seen directly by the operator. When the working implement reaches a significant length (e.g. about 120 feet), operator's visibility ceases to be reliable, regardless of the operator's visual acuity. No solution is offered in the prior art for this situation.
It is known that numerous spectral changes occur in agricultural fields over the growing season. In more lay terms, the vegetation changes color between green and dark brown, grey, yellow etc. depending on the crop maturity. The spectral variation has been shown to exist between around 360 and 1000 nm. Further, the illumination of the field can change significantly over time.
The possibilities of television are well known. In theory, it should be possible to provide a good television-based solution to enable the operator to evaluate the proximity of a specific remote part (e.g. the end of the long spraying boom) of the equipment to a pre-arranged boundary, e.g. a foam marker. However, the solution is much too sophisticated and expensive, and not compatible with the ruggedness of agricultural environment. It is important that any equipment intended to help the operator to determine the position of the boundary at a distant location (at the end of an implement etc.) is reliable but rugged enough to withstand the vibration, dust, dirt and shocks typical to the operation of agricultural equipment. In balancing the precision of the equipment and its cost, the latter factor should be given a clear preference. As mentioned above, the spectral properties of the soil and vegetation and illumination changes should also be accounted for.